Equitable and accessible classrooms should engage all learners with mathematics content in meaningful ways. However, practicing teachers need support from professional development (PD) to learn to teach with this ambitious vision. Informed by sociocultural theory, we employed an evaluative case study methodology to describe, explain, and assess the experiences of one middle school mathematics teacher's longitudinal participation in a continuous PD model focused on the Teaching for Robust Understanding (TRU) framework. Based on classroom observations and interview data, our findings show evidence of TRU-aligned changes in teaching practice as a result of years of participation in the PD model. These findings strengthen the call for PD programs focused on equity and access and suggest design elements of such PD to support effectiveness. [For the complete proceedings, see ED657822.]